1. Field of the Invention
The present invention relates to a lightning-resistant fastener, a cap, a fastener member, and a method for attaching the lightning-resistant fastener, which are for use in an airframe of an aircraft.
2. Description of the Related Art
In various members such as a wing, landing gear including wheels composing the airframe of an aircraft, fastener members (fasteners) are used for attaching surface panels forming the surfaces of wings and landing gears, various devices and the like to structural members.
The fastener member fastens two members by inserting a pin-shaped fastener main body into through-holes formed in both of two members to be fixed to each other, and fixing a tip end portion thereof with a fixing metal fixture.
Incidentally, in an aircraft, all possible measures against a lightning strike need to be taken. Therefore, a direct lightning strike to fastener members needs to be avoided. Further, when two members fastened with the fastener member are formed from different materials, an arc discharge (spark) occurs in the direction along the interface between the two members due to a potential difference between the two members at the time of a lightning strike. Thus, occurrence of an arc discharge at the time of a lightning strike needs to be reliably suppressed.
As shown in FIGS. 9A and 9B, the structure has been conventionally proposed, in which on an inner side of a wing 1 or the like, a cap 6 is attached in a state separated from a fastener main body 4a and a fixing metal fixture 4b of a fastener member 4 which penetrates through a first member 2 and a second member 3, and a gap 7 filled with air is formed between the fixing metal fixture 4b and the cap 6 (for example, refer to Japanese Patent Laid-Open No. 2-7398).
However, the art described in Japanese Patent Laid-Open No. 2-7398 does not provide the structure in which the cap 6 can be positioned with respect to the fastener member 4, and the attachment position of the cap 6 depends on a worker. Therefore, the center of the cap 6 and the center of the fastener member 4 are likely to be misaligned with each other. If a location arises, where a gap between the fastener member 4 and the cap 6 is small, in the air-gap 7, the function (lightning resistance) of the cap 6 reduces. If the cap 6 is attached in contact with the fastener member 4 in the worst case, the function itself of the cap 6 is likely to be seriously impaired.
Further, the cap 6 is attached to a second member 3 with an adhesive agent 9 as shown in FIG. 9A, or has an outer periphery covered with a rubber (insulating material) 10 as shown in FIG. 9B. Therefore, in the attaching site, a bonding work or a coating work of the rubber 10 is required, and the work requires much time and effort. In an aircraft, the work as described above has to be sometimes performed in the locations which have small spaces and are set far back, and workability is extremely low. In addition, such fastener members 4 are provided at several thousands to several tens of thousands spots, and therefore, reduction in workability directly leads to an increase in cost.
Furthermore, the work as described above is a so-called handwork, and the construction quality easily varies depending on a worker, which influences reliability.
Further, in the members which are not of a hollow structure, such as landing gears and ladders, both ends of the fastener member may be exposed outside the airframe, and in such a case, lightning resistance in both the ends of the fastener member needs to be secured.